Seismic data acquisition surveys include both land and seabed surveys that utilize seismic receivers arranged in a pattern or grid on either the land or seabed. The seismic receivers or seismic nodes are attached at various points along the length of a cable, and the seismic data acquisition grid is defined by placing multiple cables in spaced parallel lines. The seismic receivers can also be arranged on the sea bottom in independent nodes. The seismic sources or seismic shots are then created by towing or driving one or more seismic signal generators such as a seismic gun along tow lines or paths, e.g., shot lines, that are perpendicular to the arrangement of the parallel cables. The seismic signal generators are then actuated at multiple locations along the tow lines or paths and the resulting seismic signals are recorded at the seismic receivers on the cables or nodes. The recorded seismic signals are then processed to yield a three dimensional (3D) image of the subsurface below the seismic data acquisition grid.
One signal processing technique that has been used for 3D seismic surveys and in particular 3D wide azimuth surveys is common-offset vector (COV) binning. COV binning was introduced almost simultaneously in Vermeer G. J. O., “Creating Image Gathers in the Absence of Proper Common-Offset Gathers”, Exploration Geophysics (ASEG Conference Issue) 29, pp. 636-642 (1998), Vermeer G. J. O., “3-D Seismic Survey Design”, Society of Exploration Geophysics, Geophysical References 12 (2002) and Cary, P. W., “Common-Offset-Vector Gathers: An Alternative to Cross-Spreads for Wide-Azimuth 3D Surveys”, 69th Am. Int. Conf. and Exhib. SEG, Expanded Abstract, pp. 1496-99 (1999) as an alternative to cross-spread binning for 3D wide-azimuth surveys. Conventional cross-spread processing assumes that reflection points and common mid-points (CMPs) share the same lateral location. However, ocean-bottom data and mode-converted PS-waves violate this assumption. Corrections for illumination area distortion in COV processing of PS-waves have been proposed in Stewart and Gaiser, “Application and Interpretation of Converted Waves”, SEG Continuing Education Course (2011), Bale et al., “The Design and Application of Converted-Wave COVs”, CSEG GeoConvention, Expanded Abstract, pp. 1-6 (2013) and Gaiser, J. G., “General Definition of Reflection-Point Coverage for P- and PS-Wave COV Data”, 76th EAGE Conf. and Exhibition, Extended Abstract D202 (2014).
Common-offset vector (COV) binning provides single-fold datasets that can be migrated with surface offset and azimuth preserved. The latter allows post-migration processing such as radon demultiple or azimuthal residual moveout flattening to enhance the quality of the final stacked image. Single fold coverage enables each COV volume to produce a clean image with limited migration operator artefacts, but only for surveys with sources and receivers on the same acquisition datum and with a single mode arrival having symmetric ray paths in a flat earth (such as P-waves). Irregular subsurface illumination for dual-datum acquisition or mode-converted PS-wave data causes artifacts in migration of COV binned data, including acquisition footprints associated with the seismic receiver cables. The resulting 3D image of the subsurface contains a footprint of the seismic data acquisition seismic that obscures the 3D image of the subsurface.
Therefore, the need exists for improved methods for processing seismic data recorded using a grid of seismic sensors attached to multiple seismic cables that removes or corrects the footprint of the cables appearing in the resulting 3D image of the subsurface. These methods would utilize an improved COV process.